Conventionally, samples and reagents are often diluted in analysis for samples and in chemical reaction of various substances. Especially, in the case of dilution of trace amount of liquid, an operation method using a microplate and distributive pouring pipette or a method of using a dispensable robot device has been used. On one hand, the operation method using a microplate and a distributive pouring pipette have needed a complicated operation and an experienced experimenter. Furthermore, simple mixing operation of samples and reagents has been difficult outside of the laboratory or in a bedside for clinical laboratory test, etc.
On the other hand, dilution methods using dispensable robot devices inevitably need large-sized apparatuses, also failing in providing simpler use outdoors, in a bedside, etc.
In recent years, microfluidic devices receive attention as analysis devices for handling trace amount of liquid.
The microfluidic devices have a substrate with a size, for example, providing easier portability and easier handling. This substrate has a micro-channel structure formed therein for transporting samples, reagents, diluted solutions, etc. The above-described micro-channel structure suitably has reagent storing section, sample delivering section, diluting solution storing section, reaction chamber, mixing section, etc.
The above-described microfluidic device is usually formed using a substrate having a plane area not more than several hundreds of square centimeters, the substrate having a thickness of approximately 0.5 to 10 mm. Furthermore, the diameter of the flow path of the above-described micro-channel structure usually has an extraordinary fineness of approximately 5 micrometers to 1 mm. Here, when the flow path has a flat structure, the diameter of the micro-channel is specified by a width of the narrower width of the cross section of the first flow path. Incidentally, micro-droplets to be transported is sent with air etc., and often have a liquid drop-like shape.
Accordingly, since the micro-droplet will be transported through a micro-channel with a very small width in case of dilution of the samples and the reagents in the above-described microfluidic device, the surface tension of the micro-droplet, the wettability of the wall surface of the micro-channel, etc. have significant influence in contrast with normal flow paths for liquids to be transported. In addition, quantitative measuring of such a small amount of micro-droplet is difficult, resulting in possible problem of the necessity for complicated flow path circuit pattern.
Following patent document 1 discloses a method of forming a proteinic crystal in a laminar flow using a microfluidic device. In addition, following nonpatent document 1 discloses a method of forming a crystal from a trace amount of liquid by strict temperature control in a microfluidic device.
However, the patent document 1 and the nonpatent document 1 describe that each method described has a very small reaction field, and thereby enables highly precise control of reaction, but the methods has a problem that the introducing method of a protein solution to a crystallization section cannot provide a small dead volume.
The following patent document 2 discloses a trace amount of liquid measuring structure enabling measuring of a very small amount of liquid only by a simpler structure and a simpler operation for solving the above described problems. The trace amount of liquid measuring structure described in the patent document 2 has a trace fluid measuring structure using a passive valve. This trace fluid measuring structure has a first micro-channel and a second flow path extending in a predetermined direction, respectively; a third flow path having an opening in a passage wall of the first micro-channel; and a fourth flow path that has an opening in a passage wall of the second flow path, and that connects an end of the third flow path and the second flow path, the fourth flow path being thinner than the first to the third flow path. The fourth flow path has a lower wettability as compared with that of the second flow path and the third flow path, or exhibits a relatively lower capillary force. And after a liquid introduced into the first micro-channel is sucked into the third flow path through an opening of the third flow path in a passage wall of the first micro-channel, the above-described liquid remained in the first micro-channel is removed, allowing measuring of the liquid with a volume corresponding to the capacity of the third flow path.    Patent document 1: U.S. Pat. No. 6,409,332 specification    Patent document 2: JP,2004-163104,A    Nonpatent document 1: “Analytical Chemistry” (2002), 74, p.3505-3512